Molecularly Imprinted Polymers For Detection Of Contaminants

ABSTRACT

This disclosure relates to the field of molecularly imprinted polymers for detecting target molecules.

RELATED APPLICATIONS

This application claims the benefit of priority of U.S. ProvisionalApplication Ser. No. 61/529,505 filed Aug. 31, 2011, incorporated hereinby reference in its entirety.

BACKGROUND

Molecular imprinting is a technique that is used to produce moleculespecific receptors analogous to biological receptor binding sites.Molecular imprinting of a polymer creates a molecularly imprintedpolymer (MIP). An MIP is a polymer that is formed in the presence of atemplate molecule. The template molecule is removed and leaves acomplementary cavity behind in the MIP. The MIP formed demonstratesaffinity for the original template molecule.

Sensors for most airborne contaminants are generally active. Forexample, the sensors require pumps to draw air through a tube. Thesensors also require complex analysis after adsorption of the airbornecontaminants, and various extracted components must be separated priorto analysis. Furthermore, the sensors are not specific for a singleairborne contaminant. The sensors are also not real-time, and onlyprovide an indication of toxic levels in a post-exposure mode. Moreover,some airborne contaminants, such as cyclic volatile methyl siloxanes(cVMS), have been recognized as environmental problems, but there arecurrently no sensors available for these contaminants.

SUMMARY

This disclosure relates to the field of molecularly imprinted polymers(MIP), and more specifically relates to sensors that include MIP filmsto detect contaminants. The term contaminants as used herein may meanairborne contaminants, contaminants in a liquid solution, or both.

MIPs disclosed herein may be used for sensors and/or solid phaseextraction (SPE). Polymers used to produce the MIPs disclosed herein maybe referred to as a polymer host. Molecules disclosed herein for theproduction of the MIPs may be referred to as a template, a target, or atarget molecule.

Embodiments of the sensors provided for herein allow for the detectionof even a single kind of airborne contaminant The disclosure providesmethods to produce a sensor including a conductive MIP film. The methodsinvolve using the target molecule in the preparation of the MIP filmsand sensors comprising MIP films. When the target molecule is removed,it leaves behind a MIP with cavities that are complementary in shape andfunctionality to the target molecule, which can rebind a targetidentical to the original target molecule in those cavities.

Certain non-limiting embodiments of the MIP sensors provided for hereinhave conductive elements incorporating thinpolyaniline/polyethyleneimine (PANi/PEI) composite films prepared byspin-casting. Certain non-limiting embodiments of the MIP sensors arefor formaldehyde detection via changes in conductivity of the MIP.Significant increases in the resistance of these MIP sensor films happenupon exposure to formaldehyde vapor. The films disclosed herein areresponsive to other volatile organics, but the response of the films tonon-target molecules is significantly reduced. In certain embodimentsdisclosed herein, detection of a target molecule occurs with changes inthe resistance of the MIP. Significant increases in the resistance ofthe imprinted films occurs when exposed to a target molecule such whencompared to control films involving coating with unimprinted polymer. Ina non-limiting embodiment, polyvinylpyrrolidinone (PVPy) can be used asa polymer host in a MIP which can then coated onto conductive surfacessuch as single-walled carbon nanotubes (SWNT). In general, MIPs can becoated onto carbon nanotubes. In an embodiment, an MIP made from PVPywith cotinine as a target molecule can be coated onto SWNTs. These MIPcoated SWNTs can then be applied to a surface such as an electrode toform a sensor for the target molecule.

An embodiment of this disclosure provides for sensors that can bedeveloped to detect a wide range of target molecules using SWNTs coatedwith MIPs. In one embodiment, reusable SWNT MIP coated sensors createdfor the detection of cotinine are disclosed.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the disclosure. A further understanding ofthe nature and advantages of the present disclosure may be realized byreference to the remaining portions of the specification and thedrawings, which forms a part of this disclosure.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a simplified molecularly imprinted polymer solutionin an embodiment.

FIG. 2 is a flow chart illustrating the steps of a modified phaseinversion process for producing MIPs, in an embodiment.

FIG. 3A illustrates an exemplary test strip in an embodiment.

FIG. 3B illustrates an exemplary test strip with water spray containingcolor reagents in an embodiment.

FIG. 3C illustrates an exemplary test strip in a vial with liquid colorreagents in an embodiment.

FIG. 3D illustrates an exemplary test strip with color reagentscovalently bonded to the MIP film in an embodiment.

FIG. 4 illustrates an exemplary multi-band test strip in an embodiment.

FIG. 5 illustrates an exemplary patch tester in an embodiment.

FIG. 6 illustrates an exemplary conductive sensor including an MIP filmin an embodiment.

FIG. 7 illustrates a prototype sensor in an embodiment.

FIG. 8. Schematic diagram of the lithographic circuit for a sensor withinterdigitated electrodes:of 40 μm and a spacing of 20 μm.

FIG. 9. Schematic drawings of the vapor calibration chamber (left) andthe static test chamber (right)

FIG. 10. SEM images of 5% PANi (left) and 5% PANi/5% PEI films (right).

FIG. 11. Relative resistance as a function of temperature for exposureof the polymer film to formaldehyde in the static chamber.

FIG. 12. Plot of film response as a function of concentration (upper)and the time response of exposure of the film to a vaporized sampleformalin or approximately 170 ppm of formaldehyde (lower).

FIG. 13. Relative resistance as a function of exposure of the polymerfilm to 100% samples of formaldehyde, water and other volatile organicmolecules.

DETAILED DESCRIPTION MIP Films and Sensors

The present disclosure provides methods for producing MIPs. The polymerof a MIP contains binding sites for the target molecule. Without beingbound by theory, the target molecule binds to the binding sites in thepolymer layer via physical or chemical forces such as electrostaticinteractions, Van der Waals forces, ionic bonds or even covalent bonds.The polymer layer of the MIP may also be referred to as the polymerhost. The polymer layer (polymer host) of the MIP may contain astructural polymer component (structural component) and a conductivepolymer component (conductive component). The structural component ofthe polymer layer provides the structural support for the polymer layerof the MIP. In an embodiment, the structural component primarily formsthe binding site of the polymer host. In an embodiment, the conductivecomponent of the polymer host is a conductor of electrons and allows forthe flow of an electrical current through the polymer host.

In an embodiment, the physical property associated with the presence ofa target molecule in a MIP film is a change in the resistance of the MIPfilm with or without the target molecule bound. As used herein, a filmgenerally refers to a coating of a surface. An embodiment of a film iscoating of a surface by a polymer or MIP. In one embodiment a MIP filmis from about 1 Å to about 10,000 Å. In general, MIP film sensorfunctionality depends upon detecting differences in the resistivity ofthe MIP film as a function of the adsorption of a target molecule. In anembodiment, MIP film sensors can be tested for their ability to detectairborne contaminants by using various vapor chambers or otherwiseexposing the MIP film sensors disclosed herein to a sample of gas.

In an embodiment, the resistance, R, of the MIP films is measured with amultimeter when a constant current is being applied using two contactsto the MIP films and/or sensors.

The conductive polymer component of the polymer host provides aconductive path for the flow of current within the polymer host. In anembodiment, the polymer host consists of only a conductive component, oronly a structural component. In another embodiment, the polymer hostconsists of any percent composition of both the structural component andthe conductive component.

MIP conductive polymers include, but are not limited to, polyaniline(PANi). MIP structural polymers include, but are not limited topoly(4-vinylphenol), polyurethane, nylons, poly(2-vinylpyrole),poly(4-vinylpyridine), polyvinylpyrrolidinone (PVPy), polyethyleneimine(PEI), nylon-6 and polystyrene. Depending upon the MIP polymer ofchoice, the solvents in which the MIPs have high solubility can include,but are not limited to, alcohols, dimethylformamide, water, formic acidand chloroform. It will be appreciated by those skilled in the art thatmodification of polymers and/or solvents allow for tuning the process ofproducing MIPs to the chemistry of a target molecule.

In this disclosure, target molecules include airborne contaminants thatare volatile organic solvents. Examples of target molecules includeformaldehyde, which is an airborne contaminant from cigarette smoke andmany materials in the construction trade; cotinine, which is an airbornecontaminant from cigarette smoke; glutaraldehyde, which is used as adisinfectant in medical labs; benzopyrene, which is a polyaromatichydrocarbon from combustion; toluene and xylene, which are used in manyproducts including paints, adhesives, etc; vinyl chloride and styrene,which are monomers used in production of plastics; chemical warfareagents, such as mustards, nerve gases and phosgene; and cVMS, which arecontaminants from personal care products.

In some embodiments of the MIPs disclosed herein, homologous molecules,homologs, of the target molecule can be used instead of the targetmolecule to produce MIPs that detect the target molecule. Homologs oftarget molecules include molecules that are similar to the targetmolecule in various attributes including but not limited to size,electrostatic potentials, electronegativity, charge density, chemicalbonding potential, and molecules that have similar shapes to the targetmolecule. Homologs include isomers and stereoisomers of the targetmolecule.

Conductive polymers such as PANi are of interest as components ofelectrochemical devices and as active materials for a variety of sensingapplications. In sensors, the key feature of doped, electricallyconductive PANi is the presence of protonated nitrogen atoms that giveup the proton to an adsorbed vapor molecule, decreasing the conductanceof the polymer. Thin films optimize the density and availability ofprotonated receptor sites and minimize the diffusion distance necessaryfor the adsorbant to travel during binding events. Thin films alsoincrease the responsivity if the reporting electrode lies beneath thepolymer film.

In an embodiment, MIP films can be regenerated by extracting and/orevaporating target molecules from a MIP film by soaking or washing in asolvent in which the polymer host is insoluble, but the target moleculeis soluble. In an embodiment, the target molecules can be removed fromthe MIP binding sites through extraction and/or evaporation processes.The MIP films are then washed and dried to allow the solvent and thetarget molecule to be separated from the MIP films. After extractionand/or evaporation of the target molecule, the MIP films are ready todetect target molecule again.

Sensing using conductive polymer films can be performed either bycoating the surface of an electrode with the doped polymer, a MIPcontaining bound target molecule, and measuring the cell potential withreference to a redox electrode, or by making a true planar,chemiresistive structure. The latter can be used with a variety ofconductive polymers or composites, and may be designed to create highervalues of resistance (signal). They have the potential for rapiddetection. These planar structures may be designed with good timeresponse by an appropriate choice of geometry and materials. In someembodiments provided herein, a spin casting method for preparing thinfilms on lithographically produced electrodes and these films have beencharacterized and shown to be sensitive to target molecules in the vaporphase, also known as a gas phase or gas.

Conductivity measurements of embodiments of the sensors presented hereinare indicative of the binding of template molecules. Data are reportedas normalized resistance (or the change in resistance), referenced to aninitial or background value. The change in the resistance value, and therate of change in the resistance (the slope), are proportional to thequantity and identity of the molecule adsorbed. Either of the values maybe used to quantify and/or detect the target molecule. Additionalevidence of target molecules being bound in the MIP layer can beobtained through IR spectroscopy and gas chromatographic experiments.

The morphology of MIP films disclosed herein can be furthercharacterized by scanning electron microscopy.

MIP Coated Carbon Nanotube Films

Single-wall carbon nanotubes (SWCNTs), more generally referred to ascarbon nanotubes, exhibit a range of electrical properties dependingupon the geometry or chirality of the tube. SWCNTs contain a mixture ofmetallic and semiconducting material and, when deposited across a pairof electrodes, provide a conductive pathway. Carbon nanotubes may becoated with the insulating polymer PVPy and cast into a film, howeverthis technique has not previously been used for molecularly imprintedpolymers, MIPs.

Without being bound by theory, the mechanism for the variation in theresistance of a MIP coated carbon nanotube sensor film relies on thechemical nature of the adsorbant MIP layer and its effect on thenanotube electron energy levels. In an embodiment, the target moleculeis a nucleophile, that is, it is relatively electron rich and the MIPstructural polymer is non-conductive. The polymer coating of the carbonnanotubes decreases the conductivity of the carbon nanotubes as measuredacross the electrodes because the MIP coated, conductive nanotubes willnot be capable of good electrical contact to the metallic electrode.However, in an embodiment, the imprinted polymer contains an electronrich target molecule that, at the imprint sites, has the ability to addcharge to the electrical environment, and thus increasing theconductivity or lowering the resistance of the MIP coated carbonnanotube film.

Carbon nanotubes can be coated with MIPs. In one embodiment, the carbonnanotubes act as a conductor to an electrical current and the MIPcoating the carbon nanotube affects the conductivity of the carbonnanotubes according to whether or not a target molecule is bound withinthe MIP layer. In one embodiment, the MIPs coating the carbon nanotubescan have polymer hosts made from only structural components, for examplePYPy. In another embodiment, the MIPs coating the carbon nanotubes canhave polymer hosts made from a mixture of both conductive components andstructural components. In yet another embodiment, the MIPs coating thecarbon nanotubes can have polymer hosts made only conductive components.

In various embodiments, coating methods are provided for coatingpolymers onto carbon nanotubes. Different coating methods are modifiedto provide various and different MIP host polymers. In one embodiment,cotinine is used as the target molecule since the carbonyl group on thecotinine interacts with the hydrogen atom in the β-position with respectto the carbonyl group in PVPy to create a chemically based recognitionsite in the MIP. Because PVPy is a non-conductive polymer, the MIP-basedconductive sensor provides evidence that other non-conductive polymersmay be used to create new sensors and MIP films based on chemicalinteractions rather than only on intrinsic polymer conductivity providedby conductive polymer components.

Methods of Making MIP Films and Sensors

The present disclosure provides methods for making MIPs and sensors thatuse MIPs. In an embodiment, MIPs are made by mixing together astructural component, a conductive component, a target molecule and afirst solvent. In an embodiment, a structural component is a structuralpolymer. In an embodiment, a conductive component is a conductivepolymer. In an embodiment, the solution of the polymer components, thefirst solvent, and the target molecule is a molecularly imprintedpolymer solution. The molecularly imprinted polymer solutioncan then becoated onto a surface such as an electrode and allowed to dry. When themolecularly imprinted polymer solution is drying, the polymers form thebinding sites for the dissolved target molecules as the polymer layerpolymerizes around the target molecules. Next, the target molecule isselectively removed from the MIP layer by either evaporation of thetarget molecule or through extraction with a solvent that selectivelydissolves the target molecule, but does not dissolve the polymer host.

The solvent used in making the MIPs can boil at a lower temperature thanthe target molecule. This allows the template to form recognition sitesduring spin or dip coating. An organic solvent can then be used toremove the template. The organic solvent should be incompatible with thepolymer host to promote precipitation of the MIP. Alternatively, thevolatile organic molecule or template can be evaporated from the MIP ifthe solvent has a lower boiling point than the target.

Certain non-limiting embodiments of the MIP sensors provided for hereinhave polymer hosts containing polyaniline conductive componentsincorporated into polyethyleneimine structural components as thinPANi/PEI composite films prepared by spin-casting for formaldehydedetection via changes in conductivity. The sensors have significantincreases in the resistance of the MIP films upon exposure toformaldehyde vapor in a laboratory chamber. The films are responsive toother volatile organic vapors, but at significantly reduced levels. Themorphology of various embodiments of the MIP films have a porous surfacewell-suited to vapor phase adsorption.

There are various techniques for depositing films includingelectropolymerization, spin casting and laser deposition. In certainembodiments of the present disclosure, PANi is employed to directlymeasure the target concentration in concert with a second polymerincluded in composite materials to improve the porosity of the film.

In an embodiment, MIP films are spin-cast composites of PANi and PEI.PANi in its conductive form is insoluble, but the emeraldine base may bedissolved in several solvents in which PEI is also soluble. In anembodiment, the spin casting solution can be produced as a 5 percent (byweight) solution in each of the two polymers, structural component andconductive component.

In an embodiment, a PANi/PEI polymer layer can be spin-coated onto anelectrode. An aliquot of molecularly imprinted polymer solution isdropped onto the electrodes and allowed to spread. The spin-coaterdevice spins the electrode at a given rpm for an amount of timeresulting in the deposition of films. In an embodiment, the thickness ofthe MIP films is about 300 nm

In an embodiment MIP film sensors are constructed on oxidized siliconsubstrates with a PANi/PEI composite film as the active element abovethe electrode. In one non-limiting embodiment, prime grade siliconwafers with a thermally deposited oxide layer are used for thesubstrate. These oxide layers can be patterned by photolithography andsubsequently wet etched to produce electrodes, which are then subjectedto a vapor deposition of chromium or other metals and an overlayer ofnickel or other like metals. Lift off can be accomplished using acetone,with final rinses of water to produce an electrode patterned into aninterdigitated grid.

Methods for Making MIP Coated Carbon Nanotube Films

In an embodiment, MIP coated carbon nanotubes can be prepared bysuspending carbon nanotubes, PVPy or other polymers, and targetmolecules in a first solvent. The first solvent is then sonicated for aperiod of time. After sonication, the suspension is filtered and washedwith the first solvent in order to remove any unbound polymer or targetmolecules. The dried, MIP coated carbon nanotubes are then re-suspendedin the first solvent by sonication.

In another embodiment, the MIP contains only a structural component anda target molecule which are then coated onto carbon nanotubes. The MIPcoated carbon nanotubes are then suspended into a solution which iscoated onto a surface and allowed to dry. In an embodiment, the surfacecoated is an electrode. In another embodiment, the surface coated is asemiconductor. In yet another embodiment, the surface coated is aninsulator. In an embodiment, the target molecule in the MIP coatedcarbon nanotube film may be removed by either evaporation or throughextraction with a solvent that selectively dissolves the target moleculeand not the carbon nanotube or polymer host.

Embodiments of MIP Films and Sensors

FIG. 1 illustrates an embodiment of a simplified molecularly imprintedpolymer solution. Molecularly imprinted polymer solution 100 includes achemical component 102 dissolved in a solvent 108 and a structuralcomponent 104 also dissolved in the solvent 108. Polymer solution 100also includes target molecule 106 dissolved in solvent 108. Asillustrated in FIG. 1, target molecule 106 is bonded to the chemicalcomponent 102 in the polymer solution 100, also referred to a MIPsolution.

In an embodiment, conductive MIPs are produced by a modified phaseinversion process, as illustrated in FIG. 2. A polymer host generallyincludes a conductive component and a structural component for a targetmolecule that is present during the formation of the molecularlyimprinted polymer (MIP). For example, polyaniline is a conductivepolymer of the host, and nylon-6, polyethyleneimine, orpolyvinylpyrrolidinone may be a structural component of the polymer hostwhen these two polymers are used simultaneously. In an embodiment, thepolymer host is a conductive polymer. In one embodiment, the polymerhost is a structural polymer. In another embodiment, the MIP containsonly a structural component such as polyvinylpyrrolidinone and is castor otherwise coated upon a conductive component or surface such ascarbon nanotubes. In an embodiment, the polymer host is only aconductive polymer.

In an embodiment, a process for making MIP films of the presentdisclosure 200, also referred to as a modified phase inversion process200, includes dissolving the polymer(s), e.g., polyaniline and nylon-6,of the polymer host sequentially in a suitable solvent to form a firstsolution at step 202. After dissolution of the polymer host in thesolvent, the target molecule (e.g., formaldehyde) or a molecule withsimilar size and chemical properties as the target molecule (e.g.,formic acid and formaldehyde) is added to the first solution at step204. In an embodiment, the process 200 also includes stirring the firstsolution to insert or otherwise incorporate the target molecule into thepolymer host to form an MIP polymer solution at step 206.

In an embodiment, process 200 further includes precipitating the MIPsolution into powders at step 208 and removing the target molecule byaddition of a solvent. A suitable solvent for removal or extraction ofthe target molecule from the MIP is one in which the polymer host ispoorly soluble in, but one in which the target molecule is soluble tovery soluble in. Using the selective solubility of the target moleculeover the polymer host allows for the MIP film to act as a SPE becausethe target molecule may be selectively bound and then extracted from thepolymer host. In an embodiment, the process form making the MIP filmsdisclosed herein can be used to produce SPE powders at step 210. Afterdrying, the SPE powders are ready for use in a solid phase extraction(SPE) tube. In an embodiment, process 200 further includes storing theSPE powders or MIP film at step 216.

In another embodiment, process 200 includes casting the MIP solutioninto a film at step 212. The MIP film may or may not contain the targetmolecule. In one embodiment, the cast MIP film does not contain thetarget molecule at step 214. The MIP film can be used as a membrane oras a sensor and can be formed via any number of techniques, such as spincoating, drop casting, ink jet printing or dip coating, among others. Aspin coating procedure for an MIP film is described in the US patentpublication US 2010/0039124 A1, entitled “Molecularly Imprinted PolymerSensor Systems And Related Methods,” filed on Jun. 14, 2007, which isincorporated herein by reference. After drying, the MIP film is readyfor use in a film based sensor. In an embodiment, process 200 produces athin film MIP that can serve as part of a sensing device to detectairborne contaminants.

The interaction between a polymer host and a target molecule in a MIPcan involve non-covalent bonding, such as hydrogen bonding, between thepolymer host and the target molecule. The binding interaction canexploit other electrostatic forces in conjunction with shaperecognition, but the interaction between polymer host and the targetmolecule is not limited to non-covalent forces and can also includeionic and/or covalent chemical bonds between the target molecule and thepolymer host.

When the target molecule is removed via extraction or evaporation or byother removal means, it leaves behind a MIP with cavities that arecomplementary in shape to the target molecule and act as a binding siteto the target molecule or similar molecules. The MIP films disclosedherein are capable of rebinding target molecules through subsequentrounds of use when the MIP is regenerated between measurements byremoving the target molecule from the MIP before the next use of the MIPfilm and/or sensor.

In another embodiment, MIPs can be produced by dissolving the polymer orpolymer host components, i.e., conductive and structural, and targetmolecules in a first solvent to form a molecularly imprinted polymersolution. In one embodiment, the target molecule forms between about 1and about 30 weight percent of the molecularly imprinted polymersolution. In a preferred embodiment, the target molecule forms betweenabout 2 and about 20 weight percent of the molecularly imprinted polymersolution. In a more preferred embodiment, the target molecule formsbetween about 2 and about 15 weight percent of the molecularly imprintedpolymer solution.

In an embodiment of a MIP of the present disclosure, the molecularlyimprinted polymer solution has a molar ratio of from about 10:1 to about1:1 to about 1:10 of the structural component to the conductivecomponent. In an embodiment, the molecularly imprinted polymer solutionis from about 1 to about 30 percent of the target molecule or homolog byweight. In a preferred embodiment of a MIP of the present disclosure,the molecularly imprinted polymer solution has a molar ratio of fromabout 5:1 to about 1:1 to about 1:5 of the structural component to theconductive component. In a preferred embodiment, the molecularlyimprinted polymer solution is from about 2 to about 20 percent of thetarget molecule or homolog by weight. In a more preferred embodiment ofa MIP of the present disclosure, the molecularly imprinted polymersolution has a molar ratio of from about 1:1 of the structural componentto the conductive component. In a more preferred embodiment, themolecularly imprinted polymer solution is from about 2.5 to about 10percent of the target molecule or homolog by weight.

In an embodiment of a MIP of the present disclosure, nylon-6 is used asthe structural component and polyaniline is used as the conductivecomponent for the polymer host of a MIP film having formaldehyde as thetarget molecule. Formic acid can be used as a homolog for formaldehydein the production of a MIP film useful for the detection of formaldehydeas the target molecule. Formic acid can be used as both a solvent fordissolving the structural and conductive components as well as a homologfor the target molecule formaldehyde.

The first solvent should be suitable for each component of the polymerhost and the target molecule. For example, polyaniline, nylon andformaldehyde are soluble in formic acid. The polymer hosts and solventscan vary for a particular target molecule of interest. Non-limitingexamples of solvents can include alcohols, dimethylformamide, water,formic acid and chloroform.

In an embodiment, after dissolving the polymer host components, 2 to 10weight percent of the target molecule is added in the polymer solution,followed by stirring for about 20 hours to uniformly mix the target inthe polymer solution and form the molecularly imprinted polymersolution. In general, when a higher target concentration is used, thesensitivity of the MIP to target detection increases. However, the MIP'sdetection or separation for a particular molecule or molecularspecificity is reduced.

In an embodiment, thin films are produced by spin casting onto glasssubstrates at a spin rate of about 4000 rpm for a period of about 30seconds and allowed to air dry for about 1 hour. The final film can bestored until needed for use to rebind the target.

The MIP films produced in process 200 are suitable for use as a sensorthat reports the presence of the target molecule via, for example, acolor change, either through a polymer incorporated chromaphore or anexternally added reagent. Such a film can be built into a capacitor tomonitor dielectric changes due to the presence/absence of the targetmolecule. Alternatively, if the polymer is conductive, a resistor thatmonitors the presence of the target molecule via conductivity changescan be constructed. Conductivity can be incorporated into the MIP byusing a conductive polymer such as polyaniline and a structural polymercomponent that provides the actual recognition sites.

There are various techniques for visual identification or electricaldetection of MIPs exposed to their target molecules. These techniquescan use static adsorption, flow absorption or capillary action. FIG. 3Aillustrates an exemplary test strip 300 that includes a plasticsubstrate 302. A portion of the plastic substrate 302 is covered with anMIP film 304. FIG. 3B illustrates that a sample solution 306 can bedeposited on MIP film 304 and followed by washing sample solution 306with a water spray containing a color reagent 308A. When a targetmolecule binds to the color reagent, the test strip changes color toindicate a “Yes” for the presence of the target. Otherwise, if no targetmolecule binds to the color reagent, there is no color change, whichindicates “No” for the presence of the target. Color reagent 308A canalso provide a range of concentration of the target based upon colorintensity.

Alternatively, instead of using a water spray containing color reagent308A, test strip 300 can be used in a vial 310 with a liquid colorreagent 308B, as illustrated in FIG. 3C. One can open cap 314 of vial310, apply sample solution 306 to the MIP film 304, wash off any excesssample, and deposit test strip 300 in vial 310, followed by sealing cap314 and shaking vial 310 to monitor color change of color reagent 308B.

FIG. 3D illustrates test strip 300′ with color reagent 308C covalentlybonded to the MIP film. Color reagent 308C is also capable of covalentlybonding with a target molecule. If target sample 306 is present on theMIP film 304, color reagent 308C will change its color to indicate thedetection of the target sample.

FIG. 4 illustrates an exemplary multi-band test strip. Multi-band teststrip 400 includes a plastic substrate 402 covered with an adsorbinglayer 401 (e.g., a paper layer, such as utilized in paper chromatographystrips). Multi-band test strip 400 is useful when reagents must be addedsequentially. A liquid sample can be added at end 406 to flow throughreagent bands 402B and 404B, in the direction of arrow 403. The liquidsample flow picks up reagents 402A and 404A in reagent bands 402B and404B respectively. A final reagent band 406B includes both a reagent406A and an MIP film 408. Upon reaching reagent band 406B, if the targetis present and has reacted with reagents 402A and 404A, it will reactwith MIP film 408, and will provide a color change to indicate thepresence of the target. Otherwise, no color change occurs.

FIG. 5 illustrates a cross-sectional view of an exemplary sensor for atarget molecule. The sensor 500 includes a thin, easily broken membrane502 that is sandwiched between a reagent reservoir 504 and an MIP film506. A sample can be applied to the MIP, and excess sample can be washedoff. Sensor 500 can be twisted so that the membrane 502 breaks and thereagents from reservoir 504 flow into the MIP film 506 and react withthe target to provide color to indicate the presence of the target inthe sample. Otherwise, when there is no color, sensor 500 indicates thatthe sample does not contain the target.

All of these diagnostic methods can be “Yes” or “No” tests for thepresence of the target or one can use visual comparisons of the colorintensity or a small meter to quantitatively measure the concentrationof the target.

FIG. 6 illustrates a conductive sensor. The sensor 600 includes twoelectrodes 604A and 604B with an MIP film 606 between the electrodes.The MIP film 606 is supported by a substrate 602 between the electrodes.The substrate 602 is an insulator, for example, a plastic or a glass.There are many other possible configurations for the conductive sensor.

The MIP film can be deposited between the electrodes 604A-604B. A smallelectric current flows through the MIP film 606, so that the resistanceof the MIP film 606 can be measured. The MIP film 606 must beconductive. For example, the MIP film 606 can include a conductivepolymer, such as polyaniline. In an embodiment, the MIP film can also beformed from MIP-coated carbon nanotubes (CNTs) and/or single wall carbonnanotubes (SWNTs). The terms CNT and SWNT as used herein are generallyinterchangeable with SWNTs being a kind of CNT. The MIP-coated CNTs canbe used when it is difficult to find a conductive polymer host for aparticular target. The MIP-coated CNTs can also be used when it isdesirable to have more uniformly sized MIP powders for follow-upanalysis by techniques such as HPLC.

MIP films disclosed herein are useful as personal sensors for detectingexposure to harmful target molecules. The sensors that can be worn by auser in contact with an atmosphere that could be contaminated by targetmolecules.

In an embodiment, a MIP film personal sensor, a MIP film, and a MIP filmsensormay employ radio frequency identification (RFID) technology toreport values for exposure to the target molecule in real time. Aprototype sensor is shown in FIG. 7. A student identification card 704is on the right side of sensor 702 as a size reference. The sensor 702is a clip-on device that is about two inches by two inches by 0.25inches. For the MIP sensing elements, the MIP film thickness can beabout 0.25 inches. This is a small, easily worn device of the sameapproximate dimensions as, for example, a radiation badge. It isfeasible, using for example, ink jet printing, to create a single sensorthat has MIPs targeted to a range of organic molecules and tosimultaneously monitor all of these sensors that are still in a smallpackage by multiplexing an RFID system, which reports on the exposurelevel of a selected target in real time.

One of the benefits of the methods disclosed herein over conventionalmethods for detection of the airborne contaminants is molecularspecificity. Because of the extraction of a single contaminant, apost-analysis does not require a separation of the target from otherairborne contaminants, which will save time in follow-up analysis. Withthe uniformly sized MIP powders, the follow-up analysis using HPLC orother techniques is also simpler.

The sensor is passive, because the airborne contaminants are adsorbed bythe MIP film by exposure. There is no need for the use of a pump orother moving parts for actively drawing air into the device.

Furthermore, the sensor of the present disclosure fulfils an unmet need,as there currently exists no sensor for the detection of certainairborne contaminants. For example, the sensor as disclosed can alsoused for detection of cVMS, for which there are no sensors currentlyavailable.

Moreover, the device can provide real-time indications of exposurelevels. The device is small enough for a user to wear. It can also bedesirable to create larger versions of the sensors that can be used tomonitor a worksite, a full room or a rental space such as a hotel roomor an automobile repair shop, among others. It will be appreciated bythose skilled in the art that configuration, shape, and dimensions ofthe sensor can vary for particular applications.

Formaldehyde Sensor

In an embodiment of the MIP film sensors disclosed herein, the physicalproperty associated with the target molecule's presence in the MIP filmsis the change in the resistance of the sensing device. Reaction of thetarget molecule in a PANi/PEI MIP sensor, for example, with a protonfrom PANi reduces the conductivity of the polymer and yields thedetected signal as a change in resistivity (R). While PEI is alsoprotonated by the formic acid solvent in the preparation stage, PEI isnot conductive and is present to provide the porosity of the film.

In an embodiment, MIP sensors disclosed herein can be used to measurethe presence of airborne formaldehyde and are made with PANi/PEIpolymers using formic acid as both a solvent and as a homolog toformaldehyde. Without being bound by theory, a polymerization-initiatingstep is a feasible mechanism for adsorption of the target molecule, e.g.formaldehyde, given the pKa of formaldehyde and the chemical nature ofPANi. Formaldehyde is protonated upon reaching the surface, and thatprotonation of monomeric formaldehyde is a catalytic step in theformation of polymeric formaldehyde. In an embodiment, both componentsof a composite film such as PANi/PEI are protonated during production ofthe casting solution. In an embodiment, such as a MIP with formaldehydeas the target molecule, a single proton abstraction event withsubsequent polymerization results in the sequestering of at least twoadditional unprotonated formaldehyde molecules leading to the formationof trioxane, the simplest polymeric form of formaldehyde. This proposedmechanism implies that particular embodiments of a MIP film may adsorbsignificantly more formaldehyde than is detected.

In an embodiment, MIP sensors for formaldehyde were tested in both astatic chamber and a vapor phase chamber, see FIG. 9. Injection offormalin (37% formaldehyde) into the sample chamber elicited animmediate rise in the measured resistance. Formalin was injected intothe test chambers at different initial temperatures, providing differentvapor pressures and different vapor phase concentrations of formaldehydein air. The resistances of the MIP film sensors having formaldehyde as atarget molecule were recorded. The measured resistance of the MIP filmsensor was indicative of a response of the MIP film to formaldehyde andprovides a measure of the film sensitivity to a quantity of formaldehydein the airborne sample. Thus, in an embodiment, the MIP film sensorspresented herein can detect airborne target molecules.

The morphology of the film surface of MIP sensors produced by methodsdisclosed herein was further investigated by scanning electronmicroscopy (SEM) of MIP films produced on glass or oxidized siliconunder the coating conditions described above. FIG. 10 depicts SEM imagesof a 5 weight percent PANi film and also a 5 weight percent PANi/5weight percent PEI composite film. As depicted in FIG. 10, the pure PANifilm is very smooth, while the composite PANi/PEI film shows highlydeveloped porosity and offers significantly better responsivity to thetarget molecule. Thus, in an embodiment, the porous composite filmprovides a material for adsorption of the target molecule, e.g.formaldehyde, in the vapor/gas phase.

FIG. 11 demonstrates the responsiveness of an embodiment of a PANi/PEIMIP film to formaldehyde when formaldehyde is the target molecule. Thestatic chamber results for injections of formaldehyde over fivedifferent nominal temperatures over the range from 22° C. to 90° C. witha 5 s exposure are depicted in FIG. 11. The sample begins to cool almostimmediately upon injection causing a deviation of the fit from an exactcorrelation with temperature. In addition, there is an inherent,background, resistance for all of the sensor devices. The trend ofincreasing resistance with increasing temperature is depicted in FIG. 11and demonstrates the responsiveness of an embodiment of a MIP film toformaldehyde.

The vapor phase chamber of FIG. 9 was used to obtain a calibration of anembodiment of a MIP film sensor device having formaldehyde as the targetmolecule with respect to the amount of formaldehyde present in air. Thecomplete vaporization of the injected sample in the test chamberprovides data for calibration of the MIP sensor as follows. The gasphase concentration in air sample is calculated assuming ideal gasbehavior at a known temperature and our measurements were made at 25° C.Samples as small as 1 μL were injected, providing a minimumconcentration of vapor phase formaldehyde of 40 ppm in air. In anembodiment, this minimum sample size was not limited by the MIP filmresponse, but by the testing apparatus used.

In one embodiment, a MIP sensor device was calibrated by recording theresistance after a constant delay, post-injection. In the case of thedata presented in FIG. 12, this time delay was one minute. Also depictedin FIG. 12 is a plot of the real-time data for injection of a 5 μLsample of formalin. As further depicted in FIG. 12, the resistancecontinues to rise over the ten minute post-injection time-frame. Thus,in embodiments of the MIP film, it will continue to adsorb the targetmolecule as long sample remains in the nascent atmosphere and surfacesites in the MIP film are available. Longer measurement times generallywill provide greater signal changes.

While sensitivity is a crucial component of any sensor, a sensor shouldalso be specific or, at the least more sensitive to, the desired targetthan any interfering molecules. In one embodiment, a MIP film designedto detect formaldehyde was tested with four other molecules, and theresults are depicted in FIG. 13. FIG. 13 depicts that formaldehyde isselectively adsorbed by a MIP film sensor that has formaldehyde as atarget molecule. FIG. 13 depicts that the most significant potentialinterferent is ammonia. Ammonia is a base and is expected to havesignificant reactivity with the acidic proton on PANi and thus thePANi/PEI MIP film sensor exhibited some non-specific reactivity withammonia. As depicted in FIG. 13, the response to methanol isapproximately one-fourth that of the target formaldehyde. The responsefor water indicates that it does not significantly affect the MIP filmoperation. This observation is supported by the use of formalin as thesource of formaldehyde in embodiments of the MIP film sensor forformaldehyde discussed above where formalin, in which solutions commonlycontain from about 37% to 50% or greater water by weight, were injectedand tested as a formaldehyde source.

Carbon Nanotube MIP Sensor

In a non-limiting embodiment, carbon nanotube sensors coated with a MIPare used to measure and/or detect target molecules. Resistivitymeasurements of embodiments of sensors with MIP coated carbon nanotubeswith and without target molecules bound demonstrate the detection oftarget molecules by these MIP coated carbon nanotube sensors.Embodiments of the MIP coated carbon nanotube sensors were also testedwith molecules related to the target molecule to test the specificity ofthe MIP coated carbon nanotube sensors.

In an embodiment, MIP coated carbon nanotube films can be cast orotherwise coated upon surfaces to create target molecule specificsensors. In general, a target molecule can be dissolved in a firstsolvent along with a host polymer that is non-conductive to make astructural component only MIP solution. The structural component onlyMIP solution can then be mixed with a solution containing carbonnanotubes. The MIP and carbon nanotube solution can then be cast upon asurface, such as an electrode, forming a MIP coated carbon nanotube filmon a surface. FIG. 8 depicts an embodiment of a sensor, in the form ofan electrode, upon which MIP coated carbon nanotube films can be coated.

In a particular embodiment, films of MIP coated SWNTs using PVPy as thepolymer (with cotinine as a target molecule) and control (polymer onlywith no target molecule) coated SWNTs were deposited on the electrodesdepicted in FIG. 8 and the resistance of these devices was measured. Theresistance of the MIP film with cotinine was 2.05 kΩ (similar to theresistance of the bare carbon nanotubes), and that of the unimprintedcontrol film without continine was 7.18 kΩ, a 250% difference. Afterextraction with toluene of the cotinine from the MIP film, theresistance increased to 6.41 kΩ, while the control film resistance wasunchanged after the same procedure.

In an embodiment, the MIP coated carbon nanotube film may be regeneratedby extracting the target molecule and then exposing the MIP coatedcarbon nanotube film to a particular gas or liquid sample to detectand/or measure for a target molecule. In one embodiment, reinsertion ofcotinine into the MIP film decreased the resistance from about 7 kΩ tonearly the original value of 2.87 kΩ.

In an embodiment, the regenerative qualities of the MIP coated carbonnanotube films were demonstrated through recycling the films throughsubsequent rounds of extraction and reinsertion of the target molecule.In an embodiment, the target molecule was cotinine and the electrodesdepicted in FIG. 8 were coated with MIP coated carbon nanotubes andcontrol coated carbon nanotubes. The MIP film resistance measured 2.25kΩ, and the control film, 7.34 kΩ, a 262% difference. In a firstregeneration, extraction of the cotinine raised the MIP film resistanceto 7.50 kΩ, and reinsertion of the cotinine lowered the resistance tonearly the original value, 2.70 kΩ. In a second regeneration, the MIPsensor exhibited a resistance of 3.69 kΩ, while the control filmresistance was 11.75 kΩ, a 218% difference. In a third regeneration, theMIP sensor resistance increased to11.11 kΩ, and after cotininereinsertion, the MIP sensor resistance decreased to 4.38 kΩ.

Thus, in an embodiment, conductive films made by spin coatingmolecularly imprinted PVPy onto SWNTs have significantly differentconductivity than SWNTs coated with pure PVPy, that is unimprintedfilms. Furthermore, in a particular embodiment, when cotinine isextracted from the MIP film, it has a conductivity value similar to thatof the control film, and when cotinine is reinserted into the MIP film,the film returns a conductivity value similar to that measured prior tocotinine extraction in toluene. Thus, in an embodiment, the MIP coatedcarbon nanotube films can be reused through subsequent rounds ofregeneration.

Non-specific changes in resistivity of the sensors described above weretested through making attempts to insert cotinine into control films byfollowing the identical procedure employed for the MIP sensors presentedabove. This test was to ensure that cotinine reinserted into the MIPsensors was not adhering onto the glass or the surface of the polymerand thus non-specifically changing the resistivity. A small decrease inmeasured resistance of cotinine exposed control carbon nanotube sensorswas observed. This change in resistance is attributed to non-specificbinding. However, the magnitude of the change is indicative of a verysmall amount of target molecule indiscriminately adsorbing to thepolymer surface in the control or sensor devices.

Using the methods disclosed herein, the MIP sensors are generally moresensitive to the target molecule than any other potential interferingmolecule. In an embodiment, a cotinine target molecule MIP coated carbonnanotube sensor film was tested against nicotine, structurally similarto cotinine, but lacking the carboxyl group on the pyrrolidine ring. Thecotinine target molecule MIP coated carbon nanotube sensor had aresistance of 4.18 kΩ. Extraction of the cotinine increased theresistance to 7.31 kΩ and attempts to insert nicotine into the sensordecreased the resistance only slightly, on the same order as thenon-specific binding discussed above, to 6.57 kΩ, demonstrating thespecificity of the cotinine target molecule MIP coated carbon nanotubesensor for cotinine detection.

The regenerative capacity of the sensors for rebinding target moleculecan be quantified by gas chromatography. In an embodiment, blank glassslides, control films and imprinted films were subjected to theextraction and reinsertion processes described above, for cotinine andthe quantity of cotinine was determined The results are shown inTable 1. The cotinine target molecule MIP coated carbon nanotube filmhad a significantly higher cotinine concentration than either the blankor control films. Almost three times as much cotinine was reinsertedinto the MIP film as into the control film. Thus, in an embodiment, thechange in conductivity of an MIP film demonstrated that the imprintedpolymer was selectively adsorbing the target molecule.

TABLE 1 GC data for insertion of cotinine into extracted films. Samplecotinine ng/mL ng cotinine Blank 750 3000 Control 1050 4200 MIP 300012000

The IR spectra of MIP and related films, unsupported by the carbonnanotubes, provided a baseline for comparison of the embodiments of thesensors presented herein. IR spectra of cotinine films revealed acarbonyl absorption band at 1675 cm-1; PVPy films exhibited a carbonylband at 1652 cm-1. The carbonyl band of the cotinine-imprinted PVPy filmwas observed at 1658 cm-1 with a significant increase in intensity,indicating an interaction between the host polymer and the template.

IR spectra of the MIP-SWNT films showed that the carbonyl bands of bothcomponents were significantly shifted to higher energy. The controlSWNT-supported PVPy band occurred at 1767 cm⁻¹ and thecotinine-imprinted MIP-SWNT band at 1769 cm-1, with a significantincrease in intensity compared with the control. This observation isconsistent with the interaction reported for a PVPy-C60 complex. The IRspectra were used as an indicator of imprinting, template extraction andmolecule insertion.

In an embodiment, based on the shift in the carboxyl adsorption peak inthe infrared spectrum of cotinine in isolated and imprinted situations,both hydrogen bonding and shape recognition occurred in the MIP films.Thus, the carbonyl group on cotinine is likely interacting with thehydrogen in the β-position, with respect to the carbonyl group in thePVPy polymer, to add a chemical component of the interaction to theshape-recognition sites in the MIP.

EXAMPLES Preparation of PANi/PEI Composite Solutions

Poly(aniline) was purchased from Polysciences, Inc. as the undoped,emeraldine base form with a molecular weight of 15,000 and aconductivity of 10e-10 S/cm. Branched poly(ethyleneimine), PEI, with amolecular weight 70,000 g/mol was obtained from Alfa-Aesar as a 30%aqueous solution. Formic acid, >98%, was purchased from EMD Chemicalsand used to dissolve the polymers prior to spin casting. Formaldehydewas purchased from Fisher Scientific as formalin solution (37%formaldehyde) containing both water and a small quantity of methanol.All reagents were used as received without any further treatment.

The polymer films for detecting formaldehyde were spin-cast compositesof PANi and PEI. PANi in its conductive form is insoluble. However, theemeraldine base may be dissolved in several solvents, including theformic acid used in this research. PEI is also soluble in formic acidand the formic acid solvent also acts as the dopant for PANi. The spincasting solution was produced as a 5% (by weight) solution in each ofthe two polymers. As a result of the inclusion of doped-PANi, protonatedsolutions are green, while solutions of the unprotonated material aredeep blue.

Construction of Conductive Devices

The conductive sensors were constructed on oxidized silicon substrateswith the PANi/PEI composite film as the active element above theelectrode. The production method is briefly outlined below and theresults depicted in FIG. 8.

Prime grade silicon wafers with a 5000 A thermally deposited oxide layerwere used for the substrate. These films were patterned byphotolithography and subsequently wet etched to produce the finalelectrodes with a total area of 376 mm2, following vapor deposition of1000 Å of chromium and the 200 Å overlayer of nickel. Lift off wasaccomplished using acetone, with final rinses of water. The electrodewas patterned into an interdigitated grid, as shown in FIG. 8, with 40μm fingers and 20 μm spacing.

Next, the PANi/PEI polymer layer was spin-coated onto the electrode. Analiquot of 1 mL of solution was dropped onto the electrodes, and allowedto spread for 20 seconds. The spin-coater was then brought up to 1800rpm for 30 seconds. This resulted in the deposition of films with atypical thickness of 300 nm. After this treatment, background resistancevalues are measured, and the sensor is ready for use in binding studies.Morphology of the thin films was investigated by scanning electronmicroscopy using a FEI Company, XL-30 ESEM-FEG field emission gunenvironmental scanning electron microscope.

Measurement Chambers

Two different test chambers were used. Schematic diagrams of the twosystems are depicted in FIG. 9 and described below. The static chamber,depicted on the right side of FIG. 9 uses the vapor pressure of themolecule over the liquid as the source of the gaseous sample, while thevapor chamber, depicted on the left side of FIG. 9, relies onevaporation of the complete sample in air after injection into thechamber well away from the film. The static sample system consists of asmall nylon box, containing spring-mounted electrodes and anapproximately 3 cm3 well that is filled via a syringe through a septum.The sensor assembly is placed on the electrodes above the well and anylon cover is secured using a torque wrench to ensure reproduciblepressure of the sensor against the spring-mounted electrodes.

Formaldehyde (1 mL) at a known temperature is injected into the well andthe response of the sensor is recorded. To follow the recovery of thesensor after exposure to formaldehyde, dry nitrogen is passed throughthe well to evaporate the sample. The change in the resistance of thesensor is measured using a multimeter connected to a laboratorycomputer.

The vapor chamber is a ˜8 L cylindrical chamber that is outfitted with afan at the bottom and a cover that allows for a sensor holder so thatthe device is located approximately halfway along the 30 cm length. Thecover also contains a port through which a microliter syringe may beinserted and a second port that allows mounting of a thermocouple.Electrical contact is made between sample device and the holder, the fanis switched on and a small quantity of formaldehyde (1-5 μL) isinjected. Evaporation of the sample is very fast and the film detectsthe vapor nearly instantly. The chamber is not evacuated prior to use,so that the formaldehyde vapor is diluted with air at atmosphericpressure. The change in resistance is monitored using the samemultimeter and computer as for the static chamber.

Sensor Response

The physical property associated with presence of the target molecule inthe film is the change in the resistance. Sensor functionality dependsupon detecting differences in this property as a function of theadsorption of the target formaldehyde molecule onto the device. Numerousfilms/devices were tested using formalin both in the small staticchamber and in the vapor chamber. The response of the sensing film topotentially interfering molecules was also examined.

The resistance, R, of the polymer film was measured with a KeithleyModel 2100 6 ½ Digit Multimeter. During the measurement, a constantcurrent of 1 mA was applied and the voltage through the film wasrecorded, providing a resistance value via Ohm's law. Total dissipatedpower within the film is less than 2 W. Four point measurements werefound unnecessary and all of the reported data were obtained using twocontacts, an inherently simpler measurement. Data were taken at a rateof 1 Hz over a period of several minutes.

The resistance increased by as much as 6 kΩ from its background valueprior to exposure through to a plateau associated with the level offormaldehyde in the static sample chamber. Larger changes in R, greaterthan 15 kΩ, were observed in the vapor system.

Preparation of MIP-SWNT Suspensions

The MIP-coated nanotubes were prepared by suspending 20 mg of SWNTs(BuckyUSA BU-202, 0.5-10 μm in length, 0.7-2.5 nm in diameter), 10 mg ofPVPy (Polysciences, Inc. Cat#:01051 MW: 40,000), and 5 μL of cotinine(Alfa Aesar L11873) in 50 mL of absolute ethanol (Deacon Laboratories,Inc.). A control suspension was produced with the identical mixtureminus the cotinine. Both suspensions were sonicated for four hours.After sonication, the suspensions were filtered through a 60 mL funnelcontaining a frit with 4.5-5 μm pores. The CNTs left on the frit werewashed five times with ethanol in order to remove any unbound PVPy orcotinine. The dried, coated CNTs were re-suspended in 20 mL of ethanolby sonication for one hour.

Coated Carbon Nanotube Sensor Production and Measurement

The conductive sensors were constructed on glass substrates usingchromium metal for the electrode and the PVPy-SWNT film as the activeelement above the electrode. The electrode was patterned into aninterdigitated grid, as depicted in FIG. 8, with 40 μm fingers and 20 μmspacing. The electrodes were produced by photolithography and theelectrode surface encompassed a total area of 376 mm2 The PVPy-SWNTlayer was spin-coated onto the interdigitated electrode. An aliquot of200 μL of the suspension was dropped onto the substrate and allowed tospread for 20 seconds. The spin-coater was then brought up to 2100 rpmfor 30 seconds and after coating the samples were baked at 60° C. for 20minutes. This resulted in the deposition of films with a consistentthickness of approximately 300 nm. After this treatment, backgroundresistance values were measured.

In order to completely extract the cotinine template, the sensors weresoaked in 5 mL of toluene for 12 hours. This was followed by a wash withfresh toluene in order to remove any cotinine that still adhered to theglass or the film surface. The films were then dried. The resistance ofthe films was re-measured to provide the cotinine-extracted value.

Reinsertion of cotinine into the MIP-SWNT films was accomplished byplacing the sensor in 5 mL of a 10% solution of cotinine in ethanol.Following this exposure, the films were washed with fresh ethanol toremove surface-adhered cotinine and then allowed to dry. Resistancemeasurements were then taken for the cotinine-reinserted values.

The resistance of the film was measured using a Fluke 8000A DigitalMultimeter. During the measurement, a constant current of 1 mA isapplied and the voltage through the film is recorded, providing aresistance value via Ohm's law. Total dissipated power within the filmis less than 2 W. Two point measurements were sufficient to signal thepresence or absence of the cotinine template molecule in the sensor.

Gas Chromatography and Infrared Spectroscopy Measurements

As a confirmation of the conductivity measurements, quantitative gaschromatography was also performed on the MIP-SWNT suspensions. TheMIP-SWNT and control SWNT suspensions were coated onto glass substratesusing the procedure described above. The cotinine extraction andreinsertion into these films followed the processes described above.Following the reinsertion, the cotinine reinserted into the film wasdetermined by a second extraction into toluene. One milliliter aliquotsof this extraction solution were then analyzed on a HP-5 columnfollowing the addition of quinoline as the internal standard andreduction of the volume to approximately 20 μL. Samples were analyzed ona Perkin Elmer Auto System XL Gas Chromatograph equipped with a flameionization detector in duplicate and compared to a standard curve.

Infrared spectroscopy was used as a test for the presence or absence ofthe cotinine template in the deposited films. Spectra were obtainedusing one-inch square substrates and following the procedure detailedabove for creating samples.

The attenuated total reflection infrared spectrum of the preparedsamples was recorded. Spectra were also obtained of films produced usingan MIP-SWNT suspension from which the cotinine had been extractedthrough the following steps: 10 mL of MIP-SWNT suspension were filtered;the nanotubes were re-suspended in 10 mL of toluene, noting thatcotinine is soluble in toluene and PVPy is not; the solution was stirredfor 30 min; the nanotubes were filtered and washed five times withtoluene; and re-suspended in 10 mL of absolute ethanol. Spectra ofcotinine-reinserted films were then obtained using thecotinine-extracted MIP-SWNTs that were re-suspended in 10 mL of a 5%cotinine in ethanol solution.

Having described several embodiments, it will be recognized by thoseskilled in the art that various modifications, alternativeconstructions, and equivalents can be used without departing from thespirit of the disclosure. Accordingly, the above description should notbe taken as limiting the scope of the disclosure.

Those skilled in the art will appreciate that the presently disclosedinstrumentalities teach by way of example and not by limitation.Therefore, the matter contained in the above description or shown in theaccompanying drawings should be interpreted as illustrative and not in alimiting sense. The following claims are intended to cover all genericand specific features described herein.

1. A sensor for the detection of an airborne target molecule comprisinga conductive molecularly imprinted polymer film and a surface, saidconductive molecularly imprinted polymer film comprising a polymer hostcomprising binding sites for said airborne target molecule, and whereinsaid conductive molecularly imprinted polymer film is coated upon saidsurface.
 2. The sensor of claim 1 wherein said surface comprises anelectrode. 3-4. (canceled)
 5. The sensor of claim 1, wherein saidconductive molecularly imprinted polymer film has a thickness equal toor less than about 0.25 inches.
 6. A method for detecting an airbornetarget molecule using a conductive molecularly imprinted polymer film orsensor of claim 1, said method comprising exposing said conductivemolecularly imprinted polymer film coated surface to a gas, air sample,and/or vapor, and measuring the resistance to the flow of an electricalcurrent applied to said conductive molecularly imprinted polymer filmcoated surface, and wherein said resistance measurement is used todetect said airborne target molecule in said gas, air sample, and/orvapor.
 7. A conductive molecularly imprinted polymer film compositioncomprising carbon nanotubes coated with a molecularly imprinted polymerlayer.
 8. (canceled)
 9. A sensor for the detection of an airborne targetmolecule comprising a conductive molecularly imprinted polymer film anda surface, said conductive molecularly imprinted polymer film comprisingcarbon nanotubes coated with a molecular imprinted polymer comprisingbinding sites for said airborne target molecule, and wherein saidconductive molecularly imprinted polymer film is coated upon saidsurface.
 10. The sensor of claim 9, wherein said surface comprises anelectrode. 11-16. (canceled)
 17. A method for producing a conductivemolecularly imprinted polymer film for detection of an airborne targetmolecule, said method comprising: dissolving a polymer host comprising astructural component and a conductive component in a first solvent toform a first solution; adding a target molecule to said first solution;mixing said target molecule into said first solution to form amolecularly imprinted polymer solution; coating said molecularlyimprinted polymer solution onto a surface; and removing said targetmolecule to form said conductive molecularly imprinted polymer film. 18.The method of claim 17, said coating comprising electropolymerization,spin casting or laser deposition.
 19. The method of claim 17, said stepof removing said target molecule comprising: extracting said targetmolecule from said conductive molecularly imprinted polymer film using asecond solvent, wherein said polymer host is insoluble in said secondsolvent, and wherein said target molecule is soluble in said secondsolvent.
 20. The method of claim 17, wherein said first solvent has aboiling point lower than the boiling point of said target molecule. 21.The method of claim 20, said step of removing said target moleculecomprising evaporating said target molecule from said conductivemolecularly imprinted polymer film.
 22. The method of claim 17, whereinsaid target molecule is selected from the group consisting essentiallyof glutaraldehyde, cotinine, benzonpyrene, toluene, xylene, vinylchloride, styrene, mustards, nerve gases, phosgene, and cyclic volatilemethyl siloxanes.
 23. The method of claim 17, wherein said targetmolecule comprises formaldehyde.
 24. The method of claim 17, whereinsaid first solvent is selected from the group consisting of alcohols,dimethylformamide, water, and chloroform.
 25. The method of claim 17,wherein said first solvent is formic acid.
 26. The method of claim 17,wherein said structural component comprises nylon-6, polyethyleneimine,polyurethane, polycarbonate and/or polyvinylpyrrolidinone.
 27. Themethod of claim 17, wherein said conductive component comprisespolyaniline, carbon nanotubes, and/or single wall carbon nanotubes. 28.The method of claim 17, wherein said polymer host comprises nylon-6 andpolyaniline.
 29. The method of claim 17, wherein said polymer hostcomprises polyethyleneimine and polyaniline.
 30. The method of claim 17,wherein said polymer host ranges from about 2 percent to about 15percent by weight with respect to said first solvent in said firstsolution.
 31. The method of claim 17, wherein said target moleculeranges from about 2 percent to about 10 percent by weight with respectto said first solvent in said molecularly imprinted polymer solution.32-34. (canceled)
 35. The method of claim 17, wherein said conductivemolecularly imprinted polymer film composition comprises a molar ratioof about 1 to 1 of said conductive component and said structuralcomponent. 36-37. (canceled)
 38. The method of claim 17, wherein saidairborne target molecule is selected from the group consisting ofglutaraldehyde, cotinine, benzopyrene, toluene, xylene, vinyl chloride,styrene, mustards, nerve gases, phosgene, and cyclic volatile methylsiloxanes.
 39. (canceled)
 40. The sensor of claim 1, wherein saidmolecularly imprinted polymer film comprises a polymer host comprising astructural component and a conductive component.